Telephone-exchange system.



B. R. GORWIN.

TELEPHONE EXCHANGE SYSTEM.

APPLIGATION FILED 0012.12, 190s. RENEWBD APR. 29, 1911.

1,033,877. Patented July 30, 1912;.

l l J J M I By ELMER R. CORWIN, OF CHICAGO, ILLINOIS, l-ISSIGrNOBL T0VCORWIN TELEPHONE MANU;

FACTURING COMPANY, OF CHICAGO, ILLINOIS, A CORPORATION OF ILLINOIS;

TELEPHONE-EXCIIANGE SYSTEM.y

Specification of Letters Patent.

Patented July 30,1912.

Application led October 12, 1908, Serial No. 457,195. Renewed April 29,1911. Serial No. 624,143.

To ad w/Lom t may concern.'

Be it known that I, ELMER R. ConwIN, citizen oi' the United States,residing at Chicago, in the county of Cook and State of Illinois, haveinvented a certain new and useful Improvement in Telephone EX- changeSystems, of which the following is a full, clear, concise, and exactdescription, reference being had to the accompanying drawings, forming apart of this specification.

My invention relates to telephoneeX- change systems and its objects andadvantages will fully appear by a description of one embodiment thereofshown in the accompanying drawing, in which- Figure 1 illustrates amultiple switchboard telephone exchange system to which the invention isadapted, though the invention is not to be limited in its application tomultiple switch-board systems. F ig. 2 is a detail of plug and jack.

I have shown at A, B two telephone substations each including a receivera, a transmitter Z), a switch-hook c, a call bell e, anda condenser ,t',the elements a Z) c being included in bridge of the telephone line,which bridge is open when the receiver is upon the switch-hook c andwhich bridge is closed by the switch-hook when relieved of the weight oft-he receiver. The elements e f are in another bridge permanently closedto alternating signaling currents but open to direct currents. The typeof sub station outfit shown is one that I have selected for the purposeof illustrating the invention, but it is to be understood that I do notlimit myself to the form of sub-station apparatus shown, for it will beobvious as the description of the invention is proceeded with, that theoperation of the system does not depend upon the peculiar sub-stationoutfit shown. The stations A B are connected to the eX- change, in theform of the invention shown, by means of metallic circuits whose limbs gand it are connected, respectively, with line springs g1 and thimblesh1, constituting spring-jacks. A plurality of spring-jacks is shown inmultiple relation with each line, the lowermost spring-jacksconstituting the answering-jacks while the remaining jacks constituteline-jacks. The limbs g and of each telephone line also terminate incontacts of an armature switch, which switch is governed in its positionby a cut-of`f relay z',

the limbs of each telephone line being normally connected by way of saidarmature switch and the contacts normally engaged thereby, with a linelamp or signal 76 and a battery 701 adapted to excite said lamp, whenthe circuit including the battery k1, the line signal 7:, the armatureswitch of the associate cut-ott relay z' and the line limbs g and 7L isclosed by the removal of the telephone receiver at a calling stationfrom its supporting switch-hook. The cut-olf relays are included ingrounded limbs extending from contact portions of the answering jacks,preferably the line thimbles. As will more fully hereinafter appear, thecut-off relays are initially included in local circuits by the plugs,while, ultimately, the circuits for said cut-off relays depend upon theline conductors that are conduct-ively connected by the switch-hooks att-he sub-stations. In order that the spring-jacks need not be providedwith more than two contact element-s g1 k1, and in order to dispensewithline relays and contacts between the lines and the jacks, I employ thenon-inductive resistances Z that connect a limb (71,) of each line withthe contact /zl of such line that has connection with the cut-off relayz', these non-conductive resistances being permanently connected and inparallel with the cut-oft' relays and permitting the passage of voicecurrents to their associate spring-jack parts, while at the same timeproperly controlling the distribution of battery current to eifect theproper operation of the cut-oit relays z', all in a manner which will beunderstood, after I have described the form of cord circuit outtillustrated. For the cord circuit, I have shown an answering plug my,and a connecting plug nhavingtips and sleeves united respectively by thetip strand 0 and the sleeve strand p, with which strands t-he cordcircuit apparatus of the form illustrated is connected. As I prefer toemploy double supervision, the cord strands 0 p are separated, so far asthe passage of straight current is concerned, by condense-rs g and 11,which, however, permit the passage of telephonie cur-rent. Upon the leftof the condensers g and r, I have shown the calling subscriberssupervisory relay s controlling an armature switch whose normal cont-actconstitutes a terminal of a display signaling device, such as a lamp s1,the other terminal of said lamp being grounded through a batyratusassociated with the called subscribers end of the cord circuit, and Iwill, t-herefore, simply rely upon the illustration of the calledsubscribers signaling apparatus to indicate its nature. There is alsoemployed any sut-able form of operators telephone outfit t and callingor ringing outfit u whose .circuit relation with the co-rd circuit iswell illustrated but need not be described.

Assuming that the calling subscriber A. has removed his receiver a fromits' switchhook, circuit is established through the line lamp Za by wayof the contacts of the armature switch of the associate cut-off relayz'. The operator, in response tothe signal conveyed by the lamp 7c, willplace herself in communication with the calling subscriber, after havinginserted the answering plug fmI into the jack of the calling` subscriber(the answering` jack, inasmuch as a multiple switch-board system hasbeen selected for illustrating the invention). The sleeve or body of theanswering plug mrst engages a contact part of the answering jack,namely, the partA 71.1, whereupon the cut-off relay z' of thecalling-subscribers line is included in a circuit that may be tracedfrom the grounded terminal of said cutoff relay, through the winding ofsaid cutoH relay, the terminal h1, the sleeve or body of the engagedanswering plug m, a part of the cord strand 7?, the armature switch ofthe supervisory relay s, the normal contact of said armature switch, thesupervisory signal device S1, the battery s2, back to said cut-olf relayz'. The cut-off relay z' being energized, the line signal lamp 7c isplaced in open circuit, so that the signal presented by said lamp iseffaced. Upon the further movement of the answering plug m within theengaged jack, the tip of said answering plug is brought into engagementwith the line spring g1, whereupon circuit is established through thesupervisory relay .s that may be traced from the grounded battery s2,through the winding of said supervisory relay, the portion of the tipstrand 0, the tip of the answering plug m, the line spring g1, the linelimb g (of the calling subscriber), the switch-hook c, receiver a,transmitter b, line limb 7L (of the calling subscriber), to the groundedcut-off relay Z corresponding to the calling subscribers line, by way ofnon-inductive resistance Z. lNhen the relay s is energized, thesupervisory signal displayed by the lamp s1 is effaced, so that thelocal circuit for the cut-off relay z' is broken at the armature switchof said supervisory relay, but the circuit of the cutort' relay of thecalling subscribers line is still maintained, owing to the establishmentof the circuit last traced through the resistance Z. This resistance Z,therefore, is an important feature of my present invention, for by itsemployment the telephonie connection between the contacts Ztl and thelimb /L of each line is preserved, while at the same time the limbs ofeach line enter into the formation o-f an alternative circuit for theassociate cut-off relay c' when the local circuit for said cut-off relayhas been ruptured by the movement of the armature switch of thesupervisory relay s from its normal Contact.

When the operator establishes connection with the called subscriber, thelocal circuit through the called subscribers cut-off relay z' isestablished, as had been the local circuit, through the callingsubscribers cut-off relay, but the alternative circuit through thecalled subscribers line is, of course, not established until the calledsubscriber removes his telephone from the switch-hook.

lt goes without saying that the supervisory lamps s1 are caused to glowwhen the associate supervisory relays are in open circuit, which is thecase when the corresponding receivers are upon their switch-hooks, andthat such supervisory lamps are included in open circuit when saidsupervisory relays are energized, which occurs when the associatereceivers are removed from their switch-hooks.

Another feature of my invention which has been generally described willnow be specifically pointed out. lt consists in using for the cut-offrelay circuits and the circuits for the supervisory signal devices s1, aportion of the cord strand p as well as a part of an associate lineconductor intervening between the associate contact /Ll and theresistance Z. Said line conductor portion and cord circuit portion areincluded yin local circuit in order to operatethe signal device shownand the associatecut-off relay z', the cord strand then being incompletefor talking purposes, owing to the break in. the talking strand p at thearmature switch of the supervisory relay s. Zhen the alternative circuitby way of the line for the cutolf relay z', has been established, andthe supervisory signaling device s1 has been excluded from circuit, thenthe function of the conductor 79 as a signal circuit conductor has beendischarged and its function as a part of the talking circuit is thenbrought about. It will be understood from the description that has beengiven that were it not for the interposition of each resistance Zbetween the associate line limb Z1. and the conductor unitingthe'associate thimbles Ztl associated with said associate cnt-off relayz',

current from the battery s2 would be shunted by said cut-od' relay tothe ground that must be provided in practice in connection with abattery and with which ground a terminal of the cut-off relay isconnected.

It will be observed that the resistances Z are in parallel with theassociate cut-o relays 2', in order that the function of said resistancemay be accomplished.

It is obvious that changes may readily be made in the preferredembodiment of the invention herein shown and particularly described,without departing from the spirit of the invention, and I do not,therefore, wish to be limited to the precise features illustrated, but,

Having thus described my invention, l claim as new and desire to secureby Letters Patent l. A telephone exchange system including metallictelephone lines extending to jack switches at an exchange, line signaldevices at the exchange, switching means at the stations that areconnected with the exchange by said metallic telephone lines for openingand closing circuit through said signal devices, cut-off relays at theexchange for excluding the aforesaid line signal devices from circuit,thereby e'acing the signals occasioned by said line signal devices, eachcut-oft' relay and associate telephone line having a common ground, alocal circuit for each cut-off relay including a line contact of anassociate jack switch and a plug contact for engagement with said jackswitch terminal and a grounded source of current, a resistanceinterposed between each cut-off relay and the associate line limb whichis in connection with said jack terminal that is connected with saidcut-oft1 relay, whereby in establishing connection between a ack switchand a plug, all of the current flowing from said grounded source ofcurrent is not permitted to pass to the grounded connection of theassociate telephone line, but suiiicient current is forced to passthrough the associate cut-olf relay to cause its energization, andthereby the effacement of the line signal.

2. A telephone exchange system including telephone lines connected withjack switches at an exchange, line signal devices at the exchange,switching means at the stations that are connected with t-he exchange bysaid telephone lines for opening and closing circuit through said signaldevices, a resistance interposed between a side of each telephone lineand a line terminal contact of a jack associated with said line, acutoftn relay in association with each telephone line and in parallelwith the associate resistance for excluding the aforesaid line signaldevices from circuit, thereby to efface the line signals occasioned bysaid line signal devices, a cord circuit including a plug,

a source of current, and a circuit established by said plug when engagedwith a jack and including said source of current and cut-ofi' relay,said resistance forcing the passage of sufficient current from saidsource through the cut-ofiz relay brought into association with saidplug to cause the energization of said cut-ofi relay, and thereby theeffacement of the line signal.

3. A telephone exchange system including metallic telephone linesconnected with jack switches at an exchange, line signal devices at theexchange, switching means at the stations that are connected with theexchange by said telephone lines for opening and closing circuit throughsaid signal devices, a resistance interposed between a side of eachtelephone line and a line terminal cont-act of a jack associated withsaid line, a cut-off relay in association with each telephone line andin parallel with the associate resistance for excluding the aforesaidline signal devices from circuit, thereby to efface the line signalsoccasioned by said line signal devices, a cord circuit including a plug,a source of current, and a circuit established by said plug when engagedwith a jack and including said source of current and cut-olf relay, saidresistance forcing the passage of sufficient current from said sourcethrough the cut-off relay brought int-o association with said plug tocause the energization of said cut-olf relay, and thereby the eifacementof the line signal.

it. A telephone exchange system including metallic telephone linesextending to jack switches at an exchange, line signal devices at theexchange, cut-off relays at the exchange for effacing the signalsoccasioned by said line signal devices, each cut-off relay and associatetelephone line having a common ground, a local circuit for each cut-offrelay including a line contact of an associate jack switch and a plugcontact for engagement with said jack switch terminal and a groundedsource of current, a relay and the associate line limb which is inconnection with said jack terminal that is connected with said cut-olfrelay, whereby in establishing connection between a jack switch and aplug, all of the current flowing from said grounded source of current isnot permitted to pass to the grounded connection of the associatetelephone line, but sufficient current is forced to pass through theassociate cut-0E relay to cause its energization, and thereby theeffacement of the line signal, a cord circuit relay under the control ofa telephone station, an alternate circuit for a cut-off relay, andswitching mechanism controlled by said cord circuit relay serving togovern the effectivel ness of said alternate circuit.

sistance interposed between each cut-off re- 5. A telephone exchangesystem including telephone lines connected with jack switches at anexchange, a resistance interposed between a side of each telephone lineand a line terminal contact of a jack associated with said line, acut-offl relay in association with each telephone line and in parallelwith the associate resistance, a cord circuit including a plug, a sourceof' current, a circuit established by said plug when engaged with a jackand including said source of current and cut-off relay, said resistanceforcing the passage of sutlicient current from said source through thecut-off relay brought into association with said plug to cause theenergization of' said cut-0H relay, and thereby the effacement of theline signal, a cord circuit relay under the contro-l of a telephonestation, an alternate circuit for a cut-off relay, and switchingmechanism controlled by said cord circuit relay serving to govern theeffectiveness of said alternate circuit.

6. A telephone exchange system including metallic telephone linesconnected with ack switches at an exchange, a resistance interposedbetween a side of each telephone line and a line terminal contact of ajack associated with said line, a cut-oil relay in association with eachtelephone line and in parallel with the associate resistance, a cordcircuit including a plug, a source of current, a circuit established bysaid plug whenngaged with a jack and including said source of currentand cut-off relay, said resistance forcing the passage of suflicientcurrent from said source through the cut-off relay brought intoassociation with said plug to cause the energization of said cut-off'relay, and thereby the effacement of the line signal, a cord circuitrelay under the control of a telephone station,.an alternate circuit fora cut-oft1 relay, and switching mechanism controlled by said cordcircuit relay serving to govern the effectiveness of said alternatecircuit.

7. A telephone exchange system including metallic telephone linesextending to jack switches at an exchange, line signal devices at theexchange, cut-oft1 relays at the exchange for eacing the signalsoccasioned by said line signal devices, each cut-off relay and associatetelephone line having a common ground, a local circuit for each cut-offrelay including a line contact of an associate jack switch and a plugcontact for engagement with said ack switch terminal and a groundedsource of current, a resistance interposed` between each cut-off relayand the associate line limb which is in connection with said jackterminal that is connected with said cut-off relay, whereby inestablishing connection between a jack switch and a plug, all of thecurrent liowing from said grounded source of current is not permitted topass to the grounded connection of the associate telephone line, butsutlicient current is forced to pass through the associate cut-olf relayto cause its energization, and thereby the effacement of the linesignal, a cord circuit relay under the control of a telephone station,an alternate circuit for a cuto relay, switching mechanism controlled bysaid cord circuit relay serving to govern the effectiveness of saidalternate circuit, and a supervisory signal governed in its action bysaid cord circuit relay.

S. A telephone exchange system including telephone lines connected withjack switches at an exchange, a resistance interposed between a side of'each telephone line and a line terminal contact of a jack associated'with said line, a cut-oftn relay in association with each telephone lineand in parallel with the associate resistance, a cord circuit includinga plug, a source of current, a circuit established by said plug whenengaged with a jack and including said source of current and cut-ofrelay, said resistance forcing the passage of suiiicient current fromsaid source through the cut-off relay brought into association with saidplug to cause the energization of said cut-ofi' relay, and thereby theeli'acement of the line signal, a cord circuit relay under the controlof a telephone station, an alternate circuit for a cutoff relay,switching mechanism controlled by said cord circuit relay serving togovern the effectiveness of said alternate circuit, and a supervisorysignal governed in its action by said cord circuit relay.

9. A telephone exchange system including metallic telephone linesconnected with jack switches at an exchange, a resistance interposedbetween a side of each telephone line and a line terminal contact of ajack associated with said line, a cut-olf relay in association with eachtelephone line and in parallel with the associate resistance, a cordcircuit including a plug, a source of current, a circuit established bysaid plug when engaged with a jack and including said source of currentand cut-oft relay, said resist-ance forcing the passage of suiiicientcurrent from said source through the cut-olf relay brought intoassociation with said plug to cause the energization of said cut-offrelay, and thereby the effacement of the line signal, a cord circuitrelay under the control of a telephone station, an alternate circuit fora cut-off relay, switching mechanism controlled by said cord circuitrelay serving to govern the effectiveness of said alternate circuit, anda supervisory signal governed in its action by said cord circuit relay.

10. A telephone exchange system including metallic telephone linesextending to jack switches at an exchange, line signal devices at theexchange, cut-olf relays at the exchange for effacing the signalsoccasioned by said line signal devices, each cutoff relay and associatetelephone line having a common ground, a local circuit for each cut-offrelay including a line contact of an associate ack switch and a plugcontact for engagement with said ack switch terminal and a groundedsource of current, a resistance interposed between each cut-ntll relayand the associate line limb which is in connection with said jackterminal that is connected with said cut-off relay, whereby inestablishing connection between a jack switch and a plug, all of thecurrent flowing from said grounded source of current is not permitted topass to the grounded connection of the associate telephone line, butsufficient current is forced to pass through the associate cut-off relayto cause its energization, and thereby the effacement of the linesignal, a cord circuit relay under the control of a telephone station,an alter'- nate circuit for a cut-oftz relay, switching mechanismcontrolled by said cord circuit relay serving to govern theeifectiveness of said alternate circuit, and a supervisory signalgoverned in its action by said cord circuit relay and included incircuit with the cut-offl relay that is brought into association with acord circuit plug and excluded from said circuit by said cord circuitrelay upo-n the establishment of the alternative circuit for thecut-ofi1 relay.

l1. A telephone exchange system including telephone lines connected withjack switches at an exchange, a resistance interposed between a side ofeach telephone line and a line terminal Contact of a jack associatedwith said line, a cut-off relay in association with each telephone lineand in parallel with the associate resistance, a cord circuit includinga plug, a source of current, a circuit established by said plug whenengaged with a ack and including said source of current and cut-oii'relay, said resistance forcing the passage of sufficient current fromsaid source through the cut-off relay brought into association with saidplug to cause the energization of said cut-oif relay, and thereby theeffacement of the line signal, a cord circuit relay under the control ofa telephone stat-ion, an alternate circuit for a cut-off relay,switching mechanism controlled by said cord circuit relay serving togovern the eectiveness of said alternate circuit, and a supervisorysignal governed in its action by said cord circuit and included incircuit with the cut-off relay that is brought into association with acord circuit plug and excluded from said circuit by said cord circuitrelay upon the establishment of the alternative circuit for the cutoffrelay.

12. A telephone exchange system including metallic telephone linesconnected with jack switches at an exchange, a resistance interposedbetween a side of each telephone line and a line terminal conta-ct of ajack associated. with said line, a cut-olf relay in association witheach telephone line and in parallel with the associate resistance, acord circuit including a plug, a source of current, a circuitestablished by said plug when engaged with a jack and including saidsource of current and cut-ntf relay, said resistance forcing the passageof suflicient current from said source through the cut-oif relay broughtinto association with said plug to cause the energization of saidcut-off relay, and thereby the effacement of the linevsignal, a cordcircuit relay under the control of a telephone station, an alternatecircuit for a cut-off relay, switching mechanism controlled by said cordcircuit relay serving to govern the effectiveness of said alternatecircuit, and a supervisory signal governed in its action by said cordcircuit relay and included in circuit with the cut-o relay that isbrought into association with a cord circuit plug and excluded from saidcircuit by said cord circuit relay upon the establishment of thealternative circuit for the cut-off relay.

18. A telephone exchange system including metallic telephone linesextending to jack switches at an exchange, line signal devices at theexchange, switching means at the stations that are connected with theexchange by said metallic telephone lines for opening and closingcircuit through said signal devices, cut-off relays at the exchange forexcluding the aforesaid line signal devices from circuit, thereby eacingthe signals occasioned by said line signal devices, each cut-off relayand associate telephone line having a common ground, a local circuit foreach cut-oftl relay including a line contact of an associate jack switchand a plug contact ,for engagement with said ack switch terminal and agrounded source of current, a resistance interposed between each cut-offrelay and the associate line limb which is in connection with said jackterminal that is connected with said cut-off relay, whereby inestablishing connection between a jack switch and a plug, all of thecurrent flowing from said grounded source of current is not permitted topass to the grounded connection of the associate telephone line, butsuflicient current is forced to pass through the associate cut-off relayto cause its energization, and thereby the eifacement of the linesignal, a cord circuit relay under the control of a telephone station,an alternate circuit for a cut-off relay, and switching mechanismcontrolled by said cord circuit relay serving to govern theeffectiveness of said alternate circuit.

14. A telephone exchange system including telephone lines connected withjack switches at an exchange, line signal devices at the exchange,switching means at the stations that are connected with the exchange bysaid telephone lines for opening and closing circuit through said signaldevices, a resistance interposed between a side of each telephone lineand a line terminal contact of a jack associated with said line, acut-off relay in association with each telephone line and in parallelwith the associate resistance for excluding the aforesaid line signaldevices from circuit, thereby to efface the line signals occasioned bysaid line signal devices, a cord circuit including a plug, a source ofcurrent, a circuit established by said plug when engaged with a jack andincluding said source of current and cut-off relay, said resistanceforcing t-he passage of suiiicient current from said source through thecut-off relay brought into association with said plug to cause theenergization of said cut-ofir1 relay, and thereby the effacement of theline signal, a cord circuit relay under the control of a telephonestation, an alternate circuit for a cutoff relay, and switchingmechanism controlled by said cord circuit relay serving to govern theeffectiveness of said alternate circuit.

15. A telephone exchange system including metallic telephone linesconnected with jack switches at an exchange, line signal devices at theexchange, switching means at the stations that are connected with theexchange by said telephone lines for opening and closing circuit throughsaid signal devices, a resistance interposed between a side of eachtelephone line and a line terminal Contact of a jack associated withsaid line, a cut-oit relay in association with each telephone line andin parallel with the associate resistance for excluding the aforesaidline signal devices from circuit, thereby to efface the line signalsoccasioned by said line signal devices, a cord circuitincluding aplug, asource of current, a circuit established by said plug when engaged witha jack and including said source of current and cut-off relay, saidresistance forcing the passage of sufhcient current from said sourcethrough the cut-off relay brought into association with said plug tocause the energization of said cut-oil1 relay, and thereby theeffacement of the line signal, a cord circuit relay under the control ofa telephone station, an alternate circuit for a cut-off relay, andswitching mechanism controlled by said cord circuit relay serving togovern the effectiveness of said alternate circuit.

16. A telephone exchange system including metallic telephone linesextending to jack switches at an exchange, line signal devices at theexchange, switching means at the stations that are connected' with theexchange by said metallic telephone lines for opening and closingcircuit through said signal devices, cut off relays at the exchange forexcluding the aforesaid line signal devices from circuit, therebyeffacing the signals occasioned by said line signal devices, eachcut-off relay and associate telephone line having a common ground, alocal circuit for each cut-off relay including a line contact of anassociate jack switch and a plug cont-act for engagement with said jackswitch terminal and a grounded source of current, a resistanceinterposed between each cut-off relay and the associate line limb whichis in connection with said jack terminal that is connected with saidcut-oif relay, whereby in establishing connection between a jack switchand a plug, all of the current flowing from said grounded source ofcurrent is not permitted to pass to the grounded connection of theassociate telephone line, but sufcient current is forced to pass throughthe associate cut-off relay to cause its energization, and thereby theeffacement of the line signal, a cord circuit relay under the control ofa telephone station, an alternate circuit for a cut-off relay, switchingmechanism controlled by said cord circuit relay serving to govern theeffectiveness of said alternate circuit, and a supervisory signalgoverned in its action by said cord circuit relay.

17. A telephone exchange system including telephone lines connected withjack switches at an exchange, line signal devices at the exchange,switching means at the stations that are connected with the exchange bysaid telephone lines for opening and closing circuit through said signaldevices, a resistance interposed between a side of each telephone lineand a line terminal contact of a jack associated with said line, acut-off relay in association with each telephone line and in parallelwith the associate resistance for excluding the aforesaid line signaldevices from circuit, thereby to efface the line signals occasioned bysaid line signal devices, a cord circuit including a plug, a source ofcurrent, a circuitestablished by said plug when engaged with a jack andincluding said source of current and cut-off relay, said resistanceforcing the passage of sufficient current from said source through thecut-olf relay brought into association with said plug to cause theenergization of said cut-off relay, and thereby the effacement of theline signal, a cord circuit relay under the control of a telephonestation, an alternate circuit for a cut-off relay, switching mechanismcontrolled by said cord circuit relay serving to govern theeffectiveness of said alternate circuit, and a supervisory signalrgoverned in its action by said cord circuit relay.

18. A telephone exchange system including metallic telephone linesconnected with jack switches at an exchange, line signal devices at theexchange, switching means at the stations that are connected with theexchange by said telephone lines for opening and closing circuit throughsaid signal devices, a resist-ance interposed between a side of eachtelephone line and a line terminal contact of a jack associated withsaid line, a cut-O relay in association with each telephone line and inparallel with the associate resistance for excluding the aforesoid linesignal devices from cir-- cuit, thereby to efface the line signalsoccasioned by said line signal devices, a cord circuit including a plug,a source of current, a circuit established by said plug when engagedwith a jack and including said source of current and cut-off relay, saidresistance forcing the passage of sufficient current from said sourcethrough the cutoff relay brought into association with said plug tocause the energization of said cutoff relay, and thereby the elfacementof the line signal, a cord circuit relay under the control of atelephone station, an alternate circuit for a cut-oft1 relay, switchingmechanism controlled by said cord circuit relay serving to govern theeffectiveness of said alternate circuit, and a supervisory signalgoverned in its action by said cord circuit relay.

19. A telephone exchange system including metallic telephone linesextending to jack switches at an exchange, line signal devices at theexchange, switching means at the stations that are connected with theexchange by said metallic telephone lines for opening and closingcircuit through said signal devices, cut-off relays at the exchange forexcluding the aforesaid line signal devices from circuit, therebyeffacing the signals occasioned by said line signal devices, eachcut-off relay and associate telephone line having a common ground, alocal circuit for each cut-olf relay including a line contact of anassociate jack switch and a plug contact for engagement with said jackswitch terminal and a grounded source of current, a resistanceinterposed between each cut-0H relay and the associate line limb whichis in connection with said jack terminal that is connected with saidcut-o relay, whereby in establishing connection between a jack switchand a plug, all of the current flowing from said grounded source ofcurrent is not permitted to pass to the grounded connection of theassociate telephone line, but suiiicient current is forced to passthrough the associate cut-oftV1 relay to cause its energization, andthereby the effacement of the line signal, a cord circuit relay underthe control of a telephone station, an alternate circuit for a cut-offrelay, switching mechanism controlled by said cord circuit relay servingto govern the effectiveness of said alternate circuit, and a supervisorysignal governed in its action by said cord circuit relay and included incircuit with the cut-off relay that is brought into association with acord circuit plug and excluded from said circuit by said cord circuitrelay upon the establishment of the alternative circuit for the cut-offrelay.

20. A telephone exchange system including telephone lines connected withjaclr 1 switches at an exchange, line signal devices at the exchange,switching means at the stations that are connected with the exchange bysaid telephone lines for opening and closing circuit through said signaldevices, a resistance interposed between a side of each telephone lineand a line terminal contact of a jack associated 'with said line, acut-off relay in association with each telephone line and in parallelwith the associate resistance for excluding the aforesaid line signaldevices from circuit, thereby to efface the line signals occasioned bysaid line signal devices, a cord circuit including a plug, a source ofcurrent, a circuit established by said plug when engaged with a jack andincluding said source of current and cutoli' relay, said resistanceforcing the passage of suflicient current from said source through thecut-off relay brought into association with said plug to cause theenergization of said cut-olf relay, and thereby the eacement of the linesignal, a cord circuit relay under the control of a telephone station,an alternate circuit for a cut-olf relay, switching mechanism controlledby said cord circuit relay serving to govern the effectiveness of saidalternate circuit, and a supervisory signal. governed in its action bysaid cord circuit and included in circuit with the cut-off relay that isbrought into association with a cord circuit plug and excluded from saidcircuit by said cord circuit relay upon the establishment of thealternative circuit for the cut-0E relay.

2l. A telephone exchange system including metallic telephone linesconnected with jack switches at an exchange, line signal devices at theexchange, switching means at the stations that are connected with theexchange by said telephone lines for opening and closing circuit throughsaid signal devices, a resistance interposed between a side of eachtelephone line and a line terminal contact of a jack associated withsaid line, a cut-olf relay in association with each telephone line andin parallel with the associate resistance for excluding the aforesaidline signal devices from circuit, thereby to eiace the line signalsoccasioned by said line signal devices, a cord circuit including a plug,a source of current, a circuit established by said plug when engagedwith a jack and including said source of current and cut-01T relay, saidresistance forcing the iso passage of sufficient current from saidsource through the cut-off relay brought into association With said plugto cause the energiZat-ion of said cut-ofi1 relay, and thereby theeffacement of the line signal, a cord circuit relay under the control ofa telephone station, an alternate circuit for a cut-ofi relay, switchingmechanism controlled by said cord circuit relay serving to govern theeffectiveness of said alternate circuit, and a supervisory signalgoverned in its action by said cord circuit relay and included incircuit With the cut-ofi' relay vthat is brought into association With acord circuit plug and excluded from said circuit by said cord circuitrelay upon the establishnient of the alternative circuit for the cutoirelay.

In Witness whereof, I hereunto subscribe my naine this tenth day ofOctober A. D., 1908.

ELMER R. CORl/VIN.

Wvitnesses G. L. CROGG, L. Gr. STROH.

Copies of this patent may be obtained for five cents each, by addressingthe Commissioner of Patents, Washington, D. C.

